"Rolling Stones" folder - contains "Let It Bled" folder contains all the tracks an .m3u and a cover.jpg

GMPC will show covers for some of my collection but not all. Even when a cover.jpg is present.
I can manually sellect the cover, but obviouslly I would like GMPC to recognise the cover.jpg files. How can I achieve this?

I think what is happening is that GMPC is downloading covers from Amazon or whereever and ignoring the ones I have in the directories. The albums with covers missing would be the albums taht it can not find covers for on the Internet.